Io as an emitter of 100-kev electrons

Abstract

If the surface conductivity of Jupiter's satellite Io is greater than 5 × 10−11 Ω−1 cm−1 and if the height-integrated Pederson conductivity of the Jovian ionosphere is greater than 0.6 mho, then it is likely that significant Debye and photoelectron sheaths form around Io. When the current balance condition between emitted photoelectrons and collected ambient electrons is used, the potential across the sheath can approach the 670-kV motional emf developed as Io moves through the Jovian magnetic field. The characteristic sheath thickness is estimated to be 50 km. As a result of the Debye sheath, photoelectrons emitted at the surface of Io can be accelerated to several hundred keV along the magnetic field lines and precipitate into the Jovian atmosphere with a flux of 105 el m−2 s−1 eV−1 averaged over the Io flux tube. This electron beam may carry in excess of 1010 W and may cause the decametric emissions. Also, 1024 el s−1 may be trapped on the field lines associated with Io. These electrons may cause the decimetric synchrotron emission. Variations of the electron spectra are considered as a function of Io’s orbital position accounting for the tilted dipole field.